Energy efficiency ethernet with assymetric low power idle

ABSTRACT

Energy efficient Ethernet with asymmetric low power idle. Low power idle mode is typically leveraged when both direction of a link do not have data traffic to transmit. Such a requirement reduces the application of low power idle due to the frequent existence of data traffic in only one direction. An asymmetric low power idle mode enables reduction in power consumption and signal emissions even when one direction has data traffic to transmit.

This application claims priority to provisional patent application No.61/496,607, filed Jun. 14, 2011, which is incorporated by referenceherein, in its entirety, for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to energy efficient Ethernetnetworks and, more particularly, to energy efficient Ethernet withasymmetric low power idle.

2. Introduction

Energy costs continue to escalate in a trend that has accelerated inrecent years. Such being the case, various industries have becomeincreasingly sensitive to the impact of those rising costs. One areathat has drawn increasing scrutiny is the IT infrastructure. Manycompanies are now looking at their IT systems' power usage to determinewhether the energy costs can be reduced. For this reason, an industryfocus on energy efficient networks has arisen to address the risingcosts of IT equipment usage as a whole (i.e., PCs, displays, printers,servers, network equipment, etc.).

In designing an energy efficient solution, one of the considerations isthe utilization of the network link. For example, many network links aretypically in an idle state between sporadic bursts of data. Thetransmission of idle signals on a link wastes energy and adds to theradiated emission levels. Identification of these frequent low linkutilization periods can therefore provide opportunities to produceenergy savings.

In other network links, however, the traffic profile can include regularor intermittent low-bandwidth traffic, with bursts of high-bandwidthtraffic. Here, identification of a low link utilization period is moredifficult and the potential for energy savings is reduced.

Conventionally, an energy efficiency control policy in a network deviceis operative to analyze the link utilization to determine whether toenter a low power idle mode to save power. As data from the twodifferent sides of the link do not necessarily appear at the same time,identifying an opportune time to enter a low power idle mode can bedifficult. What is needed therefore is a mechanism that can maximizeenergy savings when considering the asymmetric nature of linkutilization.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates an Ethernet link between link partners.

FIG. 2 illustrates refresh signaling between link partners in a lowpower idle mode.

FIG. 3 illustrates signaling between link partners with one-way data.

FIG. 4 illustrates usage of symmetric low power idle with asymmetricdata traffic.

FIGS. 5 and 6 illustrate usage of asymmetric low power idle withasymmetric data traffic.

FIG. 7 illustrates a flowchart of a process of the present invention.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

Energy efficient Ethernet networks attempt to save power when thetraffic utilization of the network is not at its maximum capacity. Thisserves to minimize the performance impact while maximizing energysavings. Energy efficiency can be applied asymmetrically to a link inproviding an asymmetric low power idle mode that supports aconfiguration of a physical layer device where a first direction ofcommunication is in an inactive state between a transmission of periodicrefresh signals that are configured to maintain synchronization of saidfirst direction of communication, and a second direction ofcommunication continues to communicate in an active state.

The asymmetric low power idle mode can be used for traffic profiles(e.g., video surveillance camera link) that can consistently produce anasymmetric transmission scenario where one direction of the network linkconsistently transmits data and the other direction of the network linktransmits limited amounts of data (e.g., camera control commands)infrequently. As the entry by the physical layer device into anasymmetric low power idle mode is not dependent on an absence of trafficin both directions on the network link, the asymmetric low power idlemode increases the opportunity for generating energy savings for thenetwork link.

At a broad level, the energy efficiency control policy for a particularlink in the network determines when to enter an energy saving state,what energy saving state (i.e., level of energy savings) to enter, howlong to remain in that energy saving state, what energy saving state totransition to out of the previous energy saving state, etc. In oneembodiment, energy efficiency control policies can base theseenergy-saving decisions on a combination of settings established by anIT manager and the properties of the traffic on the link itself.

FIG. 1 illustrates an example link to which an energy efficiency controlpolicy can be applied. As illustrated, the link supports communicationbetween a first link partner 110 and a second link partner 120. Invarious embodiments, link partners 110 and 120 can represent a switch,router, endpoint (e.g., server, client, VoIP phone, wireless accesspoint, etc.), or the like. As illustrated, link partner 110 includesphysical layer device (PHY) 112, media access control (MAC) 114, andhost 116, while link partner 120 includes PHY 122, MAC 124, and host126.

In general, hosts 116 and 126 may comprise suitable logic, circuitry,and/or code that may enable operability and/or functionality of the fivehighest functional layers for data packets that are to be transmittedover the link. Since each layer in the OSI model provides a service tothe immediately higher interfacing layer, MAC controllers 114 and 124may provide the necessary services to hosts 116 and 126 to ensure thatpackets are suitably formatted and communicated to PHYs 112 and 122,respectively. MAC controllers 114 and 124 may comprise suitable logic,circuitry, and/or code that may enable handling of data link layer(Layer 2) operability and/or functionality. MAC controllers 114 and 124can be configured to implement Ethernet protocols, such as those basedon the IEEE 802.3 standard, for example. PHYs 112 and 122 can beconfigured to handle physical layer requirements, which include, but arenot limited to, packetization, data transfer andserialization/deserialization (SERDES).

As FIG. 1 further illustrates, link partners 110 and 120 also includeenergy efficiency control policy entities 118 and 128, respectively. Ingeneral, energy efficiency control policy entities 118 and 128 can bedesigned to determine when to enter an energy saving state, what energysaving state (i.e., level of energy savings) to enter, how long toremain in that energy saving state, what energy saving state totransition to out of the previous energy saving state, etc.

In general, energy efficiency control policy entities 118 and 128 cancomprise suitable logic, circuitry, and/or code that may be enabled toestablish and/or implement an energy efficiency control policy for thenetwork device. In various embodiments, energy efficiency control policyentities 118 and 128 can be a logical and/or functional block which may,for example, be implemented in one or more layers, including portions ofthe PHY or enhanced PHY, MAC, switch, controller, or other subsystems inthe host, thereby enabling energy-efficiency control at one or morelayers.

It is a feature of the present invention that energy efficient Ethernetsuch as that defined by IEEE 802.3az can provide substantial energysavings through the use of an asymmetric low power idle mode. Prior todescribing the details of an asymmetric low power idle mode, adescription of a general low power idle mode is first provided.

A general low power idle mode can be entered when the transmitters onboth sides of a link enter a period of silence when there is no data tobe sent. In this scenario, both transmitters can enter a low power idlemode where both transmitters are silent except for short periods ofrefresh signaling. FIG. 2 illustrates the transmission of refreshsignaling by both ends of the link. The use of a low power idle mode isin contrast with the conventional transmission of idle signals whenthere is no data to be sent. As would be appreciated, the transmissionof conventional idle signals would consume just as much power as thetransmission of data.

For link applications such as gigabit Ethernet, the appearance oftraffic on either end of the link would require both sides of the linkto wake up. Here, one side of the link will begin to transmit data,while the other side of the link will begin to transmit idle signals.Such a scenario is illustrated in FIG. 3. One example of a trafficprofile that can consistently produce such an asymmetric transmissionscenario is a video surveillance camera link. In one direction of thevideo surveillance camera link, video information is consistentlytransmitted. In the other direction of the video surveillance cameralink, limited amounts of data (e.g., camera control commands) aretransmitted infrequently. For the latter direction, idle signals aretransmitted for the remainder of the time. As this scenario illustrates,the appearance of consistent data on one end of the link would precludethe other end of the link from entering into a low power idle mode.

The inefficiencies of such a scenario are inherent to a two-way protocolwhere the existence of data on either end of the link would preclude thelink from entering into an low power idle mode. As FIG. 4 illustrates,data sent from either end of the link will not typically appear at thesame time. In other words, there is no correlation between the arrivalof data on one end of the link with the arrival of data on the other endof the link. In the current specification of 1000BASE-T, for example,idle signals are sent during periods when the other side is sendingdata. In the present invention, it is recognized that an entry into alow power idle mode that is conditioned on the absence of data to betransmitted in both directions of the link limits the opportunities forpower savings.

In the present invention, it is recognized that an asymmetric low poweridle mode can generate significant opportunities for additional powersavings. With an asymmetric low power idle mode, there could be trafficgoing in one direction, while the other direction of transmission onlysends refresh periods and is silent in between. FIG. 5 illustrates anapplication of an asymmetric low power idle mode to a data patternsimilar to that illustrated in FIG. 4. As illustrated, even when trafficis evenly distributed, power can be saved as data in one direction mayappear in different time intervals than the other direction. Thoseperiods during which only one direction transmitted idle signals can nowbe replaced by refresh signals in an asymmetric low power idle mode. Thereplacement of normal idle signals with refresh signals that are sentperiodically after periods of inactivity represents additional energysavings on the network link.

As would be appreciated, the additional benefits afforded by theasymmetric low power idle mode is more pronounced in those cases wheretraffic appears primarily in one direction. FIG. 6 illustrates such ascenario that represents a traffic profile of an asymmetric trafficpattern such as a video surveillance link. As illustrated, entry into alow power idle mode in only one direction is enabled while the otherdirection transmits a continual stream of data. This again is incontrast to the transmission of normal idle signals in the exampleillustrated in FIG. 3.

In an asymmetric low power idle mode, two additional low power idlestates can be defined. In a first low power idle state, the transmitteris active and the receiver is in low power idle mode, while in a secondlow power idle state, the receiver is active and the transmitter is inlow power idle mode. This is in contrast to conventional low power idlemodes where both the transmitter and receiver are active, or where boththe transmitter and receiver are in low power idle mode.

In the present invention, it is recognized that new challenges exist fordigital signal processing (DSP) blocks to enables these two newasymmetric low power idle mode states. For example, consider anasymmetric low power idle state where the receiver is active and thetransmitter is in a low power idle mode. Here, when data is beingreceived, turning off the transmitter would affect echo/next responses.Thus, in one embodiment, the transmitter can be configured to send zerosuntil the echo/next cancellers buffers are filled with all zeros beforeturning off. Sending zeros during the wake up of the transmitter canalso be used to avoid initial unstable conditions of the transmitter.

In another example, consider an asymmetric low power idle state wherethe transmitter is active and the receiver is in a low power idle mode.Here, when the transmitter is active, the received echo may be largeenough to trigger an analog signal detector. Thus, in one embodiment,the signal level can be checked after the echo/next canceller forreceive signal detection. DSP adaptation may therefore need to bemanaged accordingly to respond during active and stable periods.

While not shown in the figures, there exists a sleep period when a PHYtransitions into a low power idle mode. This sleep period can beapproximately 200 μs. For gigabit Ethernet, even if a very short datapacket needs to be sent, the active period exceeds 216 μs (i.e., sleeptime (T_(s)) plus wake up time (T_(w))). For this reason, waking up onedirection of transmission to facilitate small amounts of data representsa significant inefficiency. For traffic profiles that include thetransmission of limited amounts of data at infrequent intervals, thiscan factor can greatly impact the level of energy savings that can beachieved for the network link.

In one embodiment, the refresh periods in asymmetric low power idle modecan be used for transfer of limited amounts of data. In one embodiment,a PHY can signal to the MAC (e.g., using a defined combination of RX_ER,RX_DV and RXD signals at the MAC interface) that the PHY is in a refreshcycle and is ready to send data. The MAC can then choose to use thisrefresh period for data types that are not delay sensitive. In variousexamples, the data types that could make use of the refresh periodscould be higher layer network management packets, control commands(e.g., video camera commands), uplink data during Internet browsing, orthe like. As would be appreciated, the particular mechanism by which therefresh period can communicate limited amounts of data would beimplementation dependent. For example, the refresh periods cancommunicate limited amounts of data that can be recognized using asingle refresh period sequence, or two or more refresh period sequences.

In general, the refresh period enables a fixed lower data rate logicalchannel to be built at the MAC using the PHY refresh periods. In theexample of gigabit Ethernet, the refresh periods can potentially providea slower logical link of up to 10 Mbps using the refresh periods.Significantly, the slower data link is established without having towake up the PHY. This facilitates greater energy efficiency by enablingthe one direction of transmission to remain in a low power idle mode.

In one embodiment, the PHY can include buffers that can enable acontinuous slower link at the MAC while utilizing the refresh periodsfor sending data. When in this mode, the clock between PHY and MAC canbe slower.

In general, asymmetric low power idle can reduce power consumption andradiated emissions when applied to asymmetric or other uncorrelated datatraffic patterns. The advantage of asymmetric low power idle is anincrease in those opportunities to reduce power in either a transmitteror a receiver.

Having described an asymmetric low power idle mode, reference is nowmade to the flowchart of FIG. 7, which illustrates a flowchart of aprocess using the asymmetric low power idle mode. As illustrated, theprocess begins at step 702 where a network device begins operation in anactive mode where both directions of transmission on a network linkoperate at a defined data transmission rate. For example, a 1000BASE-TPHY would have both directions operating at a 1 Gbit/s data transmissionrate.

At step 704, the network device would then monitor the link utilizationlevel of a first direction of communication while the network devicecontinues to operate in the active mode. In one embodiment, themonitoring is performed by an energy efficiency control policy that isembodied in the network device. As would be appreciated, the energyefficiency control policy can be embodied in one or more layers of thenetwork device. Here, it should be noted that the monitoring of a firstdirection of communication that is illustrated in FIG. 7 is not intendedto be exclusive of monitoring of a second direction of communication.Rather, the example of FIG. 7 is provided to illustrate an asymmetricprocess.

At step 706, it is then determined whether the link utilization levelfalls below a threshold value. As would be appreciated, the particulartype of threshold value would be dependent on the type of indicatorsused to determine the link utilization level. In one example, the linkutilization level can be determined based on traffic queue or bufferlevels, one or more device or subsystem states, application activity,etc. Regardless of the type of indicator(s) used, the monitoring of thelink utilization relative to a threshold level can be used to determinewhether an asymmetric low power idle mode can be entered by the networkdevice.

Specifically, if it is determined at step 706 that the monitored linkutilization level in the first direction of communication does not fallbelow a threshold value, then the process would continue to operate inthe active state and monitoring would continue at step 704. If, on theother hand, it is determined at step 706 that the monitored linkutilization level in the first direction of communication does fallbelow a threshold value, then the process would continue to step 708where the first direction of communication can be transitioned into alow power idle mode.

In this process, an energy efficiency control policy can produce controlsignals that would instruct the components in one direction oftransmission to enter into a low power idle mode. For example, theenergy efficiency control policy can produce control signals that wouldinstruct the transmission subsystem to enter a low power idle mode, orcan produce control signals that would instruct the receiving subsystemto enter a low power idle mode. In one embodiment, the control signalsfor transitioning into an asymmetric low power idle mode can be producedby the MAC. In another embodiment, the control signals for transitioninginto an asymmetric low power idle mode can be produced inside the PHY,which analyzes the traffic received from the MAC.

As has been described, the definition of an asymmetric low power idlemode can enhance energy savings by removing barriers to entry into a lowpower idle mode that exist due to a requirement of inactivity on bothdirections of communication.

Another embodiment of the invention may provide a machine and/orcomputer readable storage and/or medium, having stored thereon, amachine code and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

What is claimed is:
 1. A method, comprising: operating a network devicein an active mode where a physical layer device in said network devicecommunicates with a link partner over a network link at a one Gbit/stransmission rate in both directions of communication; monitoring, bysaid network device, a link utilization level for a first direction ofcommunication over said network link; and transitioning, in response tosaid monitoring, said physical layer device from said active mode to anasymmetric low power idle mode, wherein said asymmetric low power idlemode supports a configuration of said physical layer device where saidfirst direction of communication is inactive between a transmission ofperiodic refresh signals that are configured to maintain synchronizationof said first direction of communication, and said second direction ofcommunication that is opposite said first direction of communicationcontinues to communicate at said one Gbit/s transmission rate, whereinsaid periodic refresh signals used in said first direction ofcommunication while in said asymmetric low power idle mode enablescommunication of data bits that creates a fixed data rate logicalchannel having a data transmission rate lower than one Gbit/s.
 2. Themethod of claim 1, wherein said first direction of transmission istransmission from said network device to said link partner.
 3. Themethod of claim 1, wherein said first direction of transmission istransmission from said link partner to said network device.
 4. Themethod of claim 1, wherein said physical layer device is a 1000BASE-Tphysical layer device.
 5. The method of claim 1, wherein said networklink is a video surveillance camera link.
 6. The method of claim 1,wherein said fixed data rate logical channel has a 10 Mbit/s data rate.7. A method, comprising: operating a network device in an active modewhere a physical layer device in said network device supportsbi-directional communication with a link partner over a network link ata defined data transmission rate; and transitioning, in response to alink utilization level analysis, said physical layer device from saidactive mode to an asymmetric low power idle mode, wherein saidasymmetric low power idle mode supports a configuration of said physicallayer device where a first direction of communication operates at saiddefined data transmission rate and a second direction of communicationis inactive between a transmission of periodic refresh signals that areconfigured to maintain synchronization of said second direction ofcommunication, wherein said periodic refresh signals used in said seconddirection of transmission while in said asymmetric low power idle modeenables communication of data bits that creates a fixed data ratelogical channel having a maximum data rate that is lower than saiddefined data transmission rate.
 8. The method of claim 7, wherein saidfirst direction of transmission is transmission from said network deviceto said link partner.
 9. The method of claim 7, wherein said firstdirection of transmission is transmission from said link partner to saidnetwork device.
 10. The method of claim 7, wherein said physical layerdevice is a 1000BASE-T physical layer device.
 11. The method of claim 7,wherein said network link is a video surveillance camera link.
 12. Themethod of claim 7, wherein said logical channel is a fixed data ratelogical channel having a 10 Mbit/s data rate.
 13. A network device,comprising: a transmitter that is configured to transmit at a one Gbit/stransmission rate with a link partner device via a network link; areceiver that is configured to receive at said one Gbit/s transmissionrate with said link partner device via said network link; and an energyefficiency control policy that is configured to analyze a linkutilization level of a first direction of communication over a networklink that couples the network device to said link partner device, saidenergy efficiency control policy further configured to transition, inresponse to said analysis, the network device to an asymmetric low poweridle mode, wherein said asymmetric low power idle mode supports aconfiguration of said transmitter to an inactive state between atransmission of periodic refresh signals that are configured to maintainsynchronization with said link partner device, and a configuration ofsaid receiver to receive data at said one Gbit/s transmission rate,wherein said periodic refresh signals used by said transmitter in saidasymmetric low power idle mode enables communication of data bits thatcreates a fixed data rate logical channel having a data transmissionrate lower than one Gbit/s.
 14. The network device of claim 13, whereinsaid transmitter and said receiver are part of a 1000BASE-T physicallayer device.
 15. The network device of claim 13, wherein said fixeddata rate logical channel has a 10 Mbit/s data rate.